1. Field of the Invention
The present invention relates to aromatic polycarbonate resins which are useful as the photoconductive materials for use in the electrophotographic photoconductor and as the materials for use in electronic devices such as organic electroluminescent (EL) device.
In addition, the present invention also relates to an electrophotographic photoconductor comprising an electroconductive support and a photoconductive layer formed thereon comprising an aromatic polycarbonate resin provided with improved mechanical strength.
Further, the present invention relates to an electrophotographic image forming method and apparatus using the above-mentioned electrophotographic photoconductor.
Furthermore, the present invention also relates to a process cartridge in which the above-mentioned photoconductor is incorporated.
2. Discussion of Background
Conventionally known representative aromatic polycarbonate resins are obtained by allowing 2,2-bis(4-hydroxyphenyl)propane (hereinafter referred to as bisphenol A) to react with a carbonate precursor material such as phosgene or diphenylcarbonate. Such polycarbonate resins made from bisphenol A are used in many fields because of their excellent characteristics, such as high transparency, high heat resistance, high dimensional accuracy, and high mechanical strength.
For example, this kind of polycarbonate resin is intensively studied as a binder resin for use in an organic photoconductor in the field of electrophotography.
Recently organic photoconductors are used in many copying machines and printers. These organic photoconductors have a layered structure comprising a charge generation layer (CGL) and a charge transport layer (CTL) which are successively overlaid on an electroconductive support. The charge transport layer (CTL) comprises a binder resin and a low-molecular charge transport material (CTM). There are proposed many kinds of aromatic polycarbonate resins as the above-mentioned binder resins. The addition of such a low-molecular charge transport material (CTM) to the binder resin lowers the intrinsic mechanical strength of the binder resin, so that the CTL film becomes fragile. Because of the decrease of mechanical strength of the CTL, the abrasion resistance, scratch resistance, and crack resistance of the photoconductor are lowered, with the result that the durability of the photoconductor is decreased.
Although some vinyl polymers such as polyvinyl anthracene, polyvinyl pyrene and poly-N-vinylcarbazole have been studied as high-molecular photoconductive materials for forming a charge transport complex for use in the conventional organic photoconductor, such polymers are not satisfactory from the viewpoint of photosensitivity.
In addition, high-molecular materials having charge transporting properties have been also studied to eliminate the shortcomings of the above-mentioned conventional layered photoconductor. For instance, there are proposed an acrylic resin having a triphenylamine structure as reported by M. Stolka et al., in xe2x80x9cJ. Polym. Sci., vol 21, 969 (1983)xe2x80x9d; a vinyl polymer having a hydrazone structure as described in xe2x80x9cJapan Hard Copy ""89 p. 67xe2x80x9d; and polycarbonate resins having a triarylamine structure as disclosed in U.S. Pat. Nos. 4,801,517, 4,806,443, 4,806,444, 4,937,165, 4,959,288, 5,030,532, 5,034,296, and 5,080,989, and Japanese Laid-Open Patent Applications Nos. 64-9964, 3-221522, 2-304456, 4-11627, 4-175337, 4-18371, 4-31404, and 4-133065. However, any materials have not yet been put to practical use.
According to the report of xe2x80x9cPhysical Review B46 6705 (1992)xe2x80x9d by M. A. Abkowitz et al., it is confirmed that the drift mobility of a high-molecular weight charge transport material is lower than that of a low-molecular weight material by one figure. This report is based on the comparison between the photoconductor comprising a low-molecular weight tetraarylbenzidine derivative dispersed in the photoconductive layer and the one comprising a high-molecular polycarbonate having a tetraarylbenzidine structure in its molecule. The reason for this has not been clarified, but it is suggested that the photoconductor employing the high-molecular weight charge transport material produces poor results in terms of the photosensitivity and the residual potential although the mechanical strength of the photoconductor is improved.
It is therefore a first object of the present invention to provide an aromatic polycarbonate resin with improved durability, which can serve as a high-molecular charge transport material in the organic photoconductor.
A second object of the present invention is to provide an electrophotographic photoconductor with high sensitivity and high durability.
A third object of the present invention is to provide an electrophotographic image forming method using the above-mentioned electrophotographic photoconductor.
A fourth object of the present invention is to provide an electrophotographic image forming apparatus using the above-mentioned electrophotographic photoconductor.
A fifth object of the present invention is to provide an electrophotographic process cartridge including the above-mentioned electrophotographic photoconductor.
The first object of the present invention can be achieved by the following aromatic polycarbonate resins:
An aromatic polycarbonate resin comprising a structural unit of formula (1) and a structural unit of formula (2), with the relationship between the composition ratios being 0 less than k/(k+j) less than 1 when the composition ratio of the structural unit of formula (1) is k and that of the structural unit of formula (2) is j: 
wherein R1 and R2, which may be the same or different, are each an acyl group, an alkyl group having 1 to 6 carbon atoms, which may have a substituent, or an aryl group which may have a substituent; and Ar1, Ar2, and Ar3 are each a substituted or unsubstituted arylene group; 
wherein a and b are each independently an integer of 1 to 4; and R3 and R4 are each independently a halogen atom, an alkyl group having 1 to 6 carbon atoms, which may have a substituent, an alkoxyl group having 1 to 6 carbon atoms, which may have a substituent, or an aryl group which may have a substituent, and R3 and R4 may each be the same or different when a and b are each an integer of 2, 3 or 4.
An aromatic polycarbonate resin comprising a repeat unit of formula (3): 
wherein R1, R2, R3, R4, Ar1, Ar2, Ar3, a, and b are the same as those previously defined, and n is an integer of 2 to 5,000, which represents a degree of polymerization.
An aromatic polycarbonate resin comprising a structural unit of the following formula (4) and the above-mentioned structural unit of formula (2), with the relationship between the composition ratios being 0 less than k/(k+j) less than 1 when the composition ratio of the structural unit of formula (4) is k and that of the structural unit of formula (2) is j: 
wherein c and d are each independently an integer of 0 to 5; R5 and R6 are each independently a halogen atom, an alkyl group having 1 to 6 carbon atoms, which may have a substituent, an alkoxyl group having 1 to 6 carbon atoms, which may have a substituent, or an aryl group which may have a substituent, and R5 and R6 may each be the same or different when c and d are each an integer of 2, 3, 4 or 5; and Ar3 is a substituted or unsubstituted arylene group.
An aromatic polycarbonate resin comprising a repeat unit of formula (5): 
wherein a, b, c, d, R3, R4, R5, R6, and Ar3 are the same as those previously defined, and n is an integer of 2 to 5,000, which represents a degree of polymerization.
An aromatic polycarbonate resin comprising the above-mentioned structural unit of formula (1) and a structural unit of the following formula (6), with the relationship between the composition ratios being 0 less than k/(k+j) less than 1 when the composition ratio of the structural unit of formula (1) is k and that of the structural unit of formula (6) is j: 
wherein R3 and R4 are each independently a halogen atom, an alkyl group having 1 to 6 carbon atoms, which may have a substituent, an alkoxyl group having 1 to 6 carbon atoms, which may have a substituent, or an aryl group which may have a substituent; and R7 and R8 are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, which may have a substituent, an alkoxyl group having 1 to 6 carbon atoms, which may have a substituent, or an aryl group which may have a substituent.
An aromatic polycarbonate resin comprising a repeat unit of formula (7): 
wherein R1, R2, R3, R4, R7, R8, Ar1, Ar2, Ar3 and n are the same as those previously defined.
An aromatic polycarbonate resin comprising the above-mentioned structural unit of formula (4) and the above-mentioned structural unit of formula (6), with the relationship between the composition ratios being 0 less than k/(k+j) less than 1 when the composition ratio of the structural unit of formula (4) is k and that of the structural unit of formula (6) is j.
An aromatic polycarbonate resin comprising a repeat unit of formula (8): 
wherein c, d, Ar3, R3, R4, R5, R6, R7, R8 and n are the same as those previously defined.
An aromatic polycarbonate resin comprising the above-mentioned structural unit of formula (1), and a structural unit of the following formula (23), with the relationship between the composition ratios being 0 less than k/(k+j) less than 1 when the composition ratio of the structural unit of formula (1) is k and that of the structural unit of formula (23) is j: 
wherein R3 and R4 are each independently a halogen atom, an alkyl group having 1 to 6 carbon atoms, which may have a substituent, an alkoxyl group having 1 to 6 carbon atoms, which may have a substituent, or an aryl group which may have a substituent; and R9 and R10 are each independently a halogen atom, an alkyl group having 1 to 6 carbon atoms, which may have a substituent, an alkoxyl group having 1 to 6 carbon atoms, which may have a substituent, or an aryl group which may have a substituent.
An aromatic polycarbonate resin comprising a repeat unit of formula (25): 
wherein R1, R2, R3, R4, R9, R10, Ar1, Ar2, Ar3 and n are the same as those previously defined.
An aromatic polycarbonate resin comprising the above-mentioned structural unit of formula (1), and a structural unit of the following formula (24), with the relationship between the composition ratios being 0 less than k/(k+j) less than 1 when the composition ratio of the structural unit of formula (1) is k and that of the structural unit of formula (24) is j: 
wherein R3 and R4 are each independently a halogen atom, an alkyl group having 1 to 6 carbon atoms, which may have a substituent, an alkoxyl group having 1 to 6 carbon atoms, which may have a substituent, or an aryl group which may have a substituent; and R9 and R10 are each independently a halogen atom, an alkyl group having 1 to 6 carbon atoms, which may have a substituent, an alkoxyl group having 1 to 6 carbon atoms, which may have a substituent, or an aryl group which may have a substituent.
An aromatic polycarbonate resin comprising a repeat unit of formula (26): 
wherein R1, R2, R3, R4, R9, R10, Ar1, Ar2, Ar3, and n are the same as those previously defined.
An aromatic polycarbonate resin comprising the above-mentioned structural unit of formula (4), and the above-mentioned structural unit of formula (23), with the relationship between the composition ratios being 0 less than k/(k+j) less than 1 when the composition ratio of the structural unit of formula (4) is k and that of the structural unit of formula (23) is j.
An aromatic polycarbonate resin comprising a repeat unit of formula (27): 
wherein c, d, Ar3, R3, R4, R5, R6, R9, R10, and n are the same as those previously defined.
An aromatic polycarbonate resin comprising the above-mentioned structural unit of formula (4), and the above-mentioned structural unit of formula (24), with the relationship between the composition ratios being 0 less than k/(k+j) less than 1 when the composition ratio of the structural unit of formula (4) is k and that of the structural unit of formula (24) is j.
An aromatic polycarbonate resin comprising a repeat unit of formula (28): 
wherein c, d, Ar3, R3, R4, R5, R6, R9, R10, and n are the same as those previously defined.
The second object of the present invention can be achieved by an electrophotographic photoconductor comprising an electroconductive support, and a photoconductive layer formed thereon comprising as an effective component an aromatic polycarbonate resin which comprises the structural unit of formula (2) and a structural unit with charge transporting properties, each of the structural units being contained in an amount of 5 wt. % or more of the total weight of the polycarbonate resin: 
wherein a and b are each independently an integer of 1 to 4; and R3 and R4 are each independently a halogen atom, an alkyl group having 1 to 6 carbon atoms, which may have a substituent, an alkoxyl group having 1 to 6 carbon atoms, which may have a substituent, or an aryl group which may have a substituent, and R3 and R4 may each be the same or different when a and b are each an integer of 2, 3 or 4.
It is preferable that the structural unit with charge transporting properties be contained in an amount of 10 to 90 wt. % of the total weight of the polycarbonate resin in the above-mentioned electrophotographic photoconductor.
In the aforementioned electrophotographic photoconductor, the structural unit with charge transporting properties may be represented by formula (1xe2x80x2): 
wherein R11 is a hydrogen atom, an alkyl group which may have a substituent, or an aryl group which may have a substituent; Ar1 and Ar2 are each an arylene group which may have a substituent; and R12 is an aryl group which may have a substituent.
The aromatic polycarbonate resin for use in the photoconductive layer may comprise a repeat unit of formula (3xe2x80x2): 
wherein a, b, R3, R4, R11, R12, Ar1, Ar2, and n are the same as those previously defined.
Alternatively, in the electrophotographic photoconductor, the structural unit with charge transporting properties may be the above-mentioned structural unit of formula (1).
The aromatic polycarbonate resin for use in the photoconductive layer may comprise the previously mentioned repeat unit of formula (3).
The third object of the present invention can be achieved by an electrophotographic image forming method comprising the steps of charging the surface of a photoconductor, exposing the charged surface of the photoconductor to a light image corresponding to an original image to be reproduced, thereby forming a latent electrostatic image on the photoconductor, developing the latent electrostatic image to a visible image, transferring the visible image to an image receiving member, cleaning the surface of the photoconductor, and quenching the residual potential on the surface of the photoconductor, wherein the photoconductor is any of the above-mentioned photoconductors comprising the aromatic polycarbonate resin.
The fourth object of the present invention can be achieved by an electrophotographic image forming apparatus comprising a photoconductor capable of forming a latent electrostatic image thereon, charging means for charging the surface of the photoconductor, light exposure means for exposing the charged surface of the photoconductor to a light image corresponding to an original image to be reproduced, thereby forming a latent electrostatic image on the photoconductor, development means for developing the latent electrostatic image to a visible image, image transfer means for transferring the visible image to an image receiving member, cleaning means for cleaning the surface of the photoconductor, and quenching means for quenching the residual potential on the surface of the photoconductor, wherein the photoconductor is any of the above-mentioned photoconductors comprising the aromatic polycarbonate resin.
The fifth object of the present invention can be achieved by an electrophotographic process cartridge comprising an electrophotographic photoconductor capable of forming a latent electrostatic image thereon, wherein the electrophotographic photoconductor is any of the above-mentioned photoconductors comprising the aromatic polycarbonate resin.